1. Field of the Invention
The present invention relates to a method of and an apparatus for converting interlaced image data used in the National Television System Committee (NTSC) system, the phase alteration line (PAL) system, and the like, namely, an image data having a field format in which a frame consists of an even-numbered field and an odd-numbered field into image data of a resultant frame with a predetermined size.
2. Description of the Prior Art
FIG. 1 shows an outline of constitution of an image size converting apparatus described in Japanese Patent Application No. 9-347044. The apparatus includes a table generator 110, a table memory 120, an image decoder 130, an original frame buffer 140, an image converter 150, a converted image frame buffer 160, a display controller 170, and a display 180.
The table generator 110 includes a size conversion table generator 111 and a correcting position table generator 112. The table generator 111 determines a conversion ratio, e.g., a reduction ratio in accordance with an original image size and a converted image size specified by a user to generate according to the ratio a size conversion table in which lines to be thinned out are specified. The correcting position table generator 112 generates according to the conversion ratio a correcting position table in which lines on which a filtering operation (correction) is to be conducted are specified. The tables thus created are stored respectively as a size conversion table 121 and a correcting position table 122 in table memory 120.
The image decoder 130 includes an even-numbered field decoder 131 which decodes an image signal inputted thereto to store therein image data of the even-numbered field and an odd-numbered field decoder 132 which decodes an image signal inputted thereto to store therein image data of then odd-numbered field. Stored in the frame buffer 140 is one frame of original image associated with the image data of the even-numbered field and that of the odd-numbered field stored in the decoder 131 and 132, respectively.
The image converter 150 includes a size converter 151 and a filter 152. The size converter 151 reads one frame of image data from the buffer 140 and converts the data size thereof in accordance with the size conversion table 121 prepared in the table memory 120. The filter 152 reads one frame of image data from the frame buffer 140 and filters the image data according to the correcting position table 122 stored in the table memory 120. After the size conversion and the filtering operation, the image data is stored in the frame buffer 160.
The display control section 170 reads one frame of converted image data from the frame buffer 160 and presents an image of the data on the display 180 at timing to display mobile images.
In the conventional image size converting apparatus configured as above, an image signal is supplied to the original image decoder 131 and a converted size specified by the user is supplied to the table generator 110. In the table generator 110, in accordance with the conversion ratio determined by the converted size and the original image size, the size conversion table generator 111 generates a size conversion table which specifies horizontal lines to be thinned out from the original image data (frame image). Moreover, the correcting position table generator 112 generates a correcting position table which specifies horizontal lines to be filtered in the original image data (frame image). These tables are placed in the table memory 120.
On the other hand, in the image decoder 130 having received the image signal, even-numbered and odd-numbered field decoders 131 and 132 decode the input image signal and respectively stores therein image data of the even-numbered field and that of the odd-numbered field. Thereafter, one frame of the original image based on the image data of even-numbered and odd-numbered fields is stored in the frame buffer 140.
When one frame of original image data is stored in the frame buffer 140, the data is read therefrom by the image converter 150. In the image converter 150, the size converter 151 thins out horizontal lines of the original data as specified by the size conversion table 121 and the filter 152 filters horizontal lines of the original image data in accordance with the correcting position table 122.
After the thinning-out and the filtering are finished as above, the resultant image data is once written in the converted image frame buffer 160. The data is then read therefrom by the display controller 170 to be presented on the display 180.
In addition to the image size converting apparatus, as an example of such an apparatus achieving the thinning out operation and the image compression, an image size reducing apparatus is described in Japanese Patent Laid-Open No. 9-219820. In the apparatus, original image data is formed in a frame each including an odd-numbered field and an even-numbered field in an interlaced manner. To compress the data in a vertical direction with a compression rate of N/M (N less than M), the line numbers required to thin out almost uniformly (Mxe2x88x92N) lines from successive M lines in the frame are specified in each of the odd-numbered and even-numbered fields. The original data is thinned out according to the specified line numbers. In the configuration of the apparatus, the original image can be compressed through the thinning out operation while preventing deterioration in information quality of the image.
Japanese Patent Laid-Open No. 8-314421 describes a display including a liquid-crystal display panel having 234 scanning lines and an aspect ratio of 4/3. In the display, a video signal received is thinned out to be compressed with a compression ratio of 3/4. The compressed image having an aspect ratio of 16/9 is displayed in a central zone of the panel and a mask such as a black band is displayed on 30 lines respectively over and below the displayed zone of the panel.
However, the image size converting apparatuses of the prior art are attended with problems as follows.
In the apparatus of Japanese Patent Application No. 9-347044, the even-numbered and odd-numbered field decoders 131 and 132 of the image decoder 130 decode all lines of the input image signal independently of the thinning out operation conducted later by the size converter 151. Therefore, the decoder 130 decodes lines which are not to be displayed, namely, which are to be thinned out by the size converter 151. That is, the decoding time is elongated by the unnecessary decoding.
Additionally, since the size conversion table 121 and the correcting position table 122 are first generated to convert the image size according thereto, there is required a table memory to store the tables 121 and 122. This is disadvantageous in consideration of the production cost.
The above problem is also present in the apparatuses of Japanese Patent Laid-Open Nos. 9-219820 and 8-314421.
Although various proposals have been offered as technologies associated with the interlacing scanning, the above problem cannot be solved.
It is therefore an object of the present invention to provide an image converting method and an image converting apparatus in which unnecessary processing time is required for the data decoding operation, thereby solving the above problems.
Further, another object of the present invention is to provide an image converting method and an image converting apparatus in which neither the size conversion table nor the correcting position table are required.
To achieve the above object in accordance with the present invention, there is provided an image converting apparatus for converting image data having a field format in which a frame consists of a first field and a second field into image data of a resultant frame with a predetermined size. The apparatus includes first decoding means for decoding each scanning line data of the first field of the compressed image data, second decoding means for decoding scanning line data of the second field of the compressed image data-while thinning out every second line, and first storage means for storing a frame image data combined with image data decoded by the first decoding means with image data decoded by the second decoding means.
The image converting apparatus may further include correcting means for correcting a time difference between the first and second fields for the lines decoded by the second decoding means of the lines of image data read from the first storage means, and second storage means for storing therein image data undergone the correction by the correcting means, in the form of 1-frame image data.
Moreover, the image data converting apparatus may further include black line data area setting means for setting black line data areas respectively over and below the image data read from the first storage means, each of the black line data areas including lines the number of which is xe2x85x9 that of lines of all scanning line data in the frame including the first and second fields of the compressed image data, and second storage means for storing therein image data including the black line data areas, in the form of 1-frame image data.
Additionally, the second storage means may store image data, which has undergone the correction and which includes the black line data areas, in the form of 1-frame image data.
The apparatus above may further includes third decoding means for decoding compressed image data in a frame format, third storage means for storing therein image data decoded by the third decoding means, image synthesizing means for combining the image data stored in the second storage means with that stored in the third storage means and for thereby synthesizing image data, and fourth storage means for storing therein the image data synthesized by the image synthesizing means, in a form of 1-frame image data.
In accordance with the present invention, there is provided an image conversion method of converting compressed image data having a field format in which a frame consists of a first field and a second field, into image data of a frame format with a predetermined size. The method includes the steps of decoding each scanning line data of the first field of the compressed image data, decoding scanning line data of the second field of the compressed image data while thinning out every second line, and combining image data decoded for the first field with image data decoded for the second field, thereby producing frame image data.
The decoding method may further include the step of correcting a time difference between the first and second fields for the lines corresponding to the decoded lines of the second field of the combined lines of the frame image data.
In addition, the decoding method may further include the step of setting black line data areas respectively over and below the frame image data generated by combining the data decoded for the first field with that decoded for the second field, each of the black line data areas including lines the number of which is xe2x85x9 that of lines of all scanning line data in the frame including the first and second fields of the compressed image data, thereby producing image data for an image with an aspect ratio of 4/3.
The image conversion method may further include the steps of setting black line data areas respectively over and below the frame image data generated by combining the data decoded for the first field with that decoded for the second field, each of the black line data areas including lines the number of which is xe2x85x9 that of lines of all scanning line data in the frame including the first and second fields of the compressed image data, thereby producing image data for an image with an aspect ratio of 4/3, and correcting a time difference between the first and second fields for lines of image data read from the first storage means, the lines corresponding to the lines associated with the data for the second field.
In the conversion method above, there may be further included the step of combining the frame image data, which includes the black line data areas and which has undergone the correction, with the image data obtained by decoding compressed data of a frame format, thereby synthesizing one frame of image data.
As above, while each line of scanning line data of the first field is decoded, the scanning line data of the second field is thinned out on alternate lines and decoded. Consequently, the number of lines of the frame thus decoded is xc2xe of that of the frame including the first and second fields before the decoding. For example, if the frame, which has an aspect ratio of 4/3, consists the original first and second fields, the image data obtained through the decoding of the first and second decoding means has an aspect ratio of 16/9.
As described above, due to the thinning out operation, the image is minimized. Namely, the image size is converted through the decoding operation in accordance with the present invention. Therefore, the size conversion table used in the conventional technology can be dispensed with. Moreover, only the lines which are displayed later are decoded.
In accordance with the present invention, for the resultant data of the second field in which only every second line is thinned out in the decoding operation, a correction is conducted with respect to time difference between the first and second fields. In short, the correction cannot be carried out for the lines thinned out and hence the correction time is reduced. In addition, since the correcting position table of the prior art is not required in the correction, it is possible to avoid the disadvantage of increase in the production cost.
In accordance with the present invention, since neither the size conversion table nor the correcting position table is necessary, it is possible to provided an image conversion method and an image converting apparatus with a lower cost.
Furthermore, the conventional operation to decode the lines which are not to be displayed is removed in accordance with the present invention. Consequently, there can be provided an image conversion method and an image converting apparatus in which the conventional decoding operation not required is suppressed in the decoding operation.